1. Field of the Invention
The present invention relates to a nitride semiconductor light emitting diode, and more particularly, to a nitride semiconductor light emitting diode and a fabrication method thereof, in which a high reflectivity layer is formed to minimize light loss as well as achieve excellent electrostatic discharge characteristics.
2. Description of the Related Art
As well-known in the art, Nitride semiconductor Light Emitting Diodes (LEDs) are being spotlighted as high power optical devices capable of generating single wavelength light such as blue or green light to realize full color display. A nitride semiconductor LED is made by growing single crystal semiconductor expressed as a formula of AlxInyGa(1-x-y)N (wherein 0≦x≦1, 0≦y≦1 and 0≦x+y≦1) on a specific substrate of for example sapphire for growing GaN.
Unlike a GaAs-based red LED that has electrodes formed on the underside of a substrate, the sapphire substrate as a representative substrate for growing GaN has two electrodes formed on crystallized semiconductor layers as shown in FIG. 1a because it is insulated.
Referring to FIG. 1a, a nitride semiconductor LED 10 includes a sapphire substrate 11, a first nitride semiconductor layer 13, an active layer 15 and a second nitride semiconductor layer 17 formed in their order on the sapphire substrate 11. Further, in order to form two electrodes on the semiconductor layers as described above, predetermined regions of the second nitride semiconductor layer 17 and the active layer 15 are etched to form a general mesa structure. The first electrode 18a is arranged on the exposed region of the first nitride semiconductor layer 13, and the second electrode 18b is arranged on the second nitride semiconductor 17.
The nitride semiconductor LED 10, as shown in FIG. 1a, can be loaded on a Printed Circuit Board (PCB) 21 and then covered with resin 28 to form an LED package 20. A circuit pattern including first and second conductive patterns 22a and 22b are formed on the PCB 21, the LED 10 is attached to the second conductive pattern 22b via a conductive paste layer 16, and the electrodes 18b and 18a of the LED 10 are connected to the first and second conductive patterns 22a and 22b via the wires 24a and 24b. 
In the package shown in FIG. 1b, light rays generated from the nitride semiconductor LED are projected not only in desirable upward directions but also in downward directions through the transparent sapphire substrate. Light rays directed downward are partially absorbed and extinguished or partially reach the conductive paste layer 16 bonding the LED 10 with the second conductive pattern 22b that reflects the light rays upward. However, because the conductive paste layer 16 itself does not define an irregular surface, high reflectivity can be rarely expected from the conductive paste layer 16 even though it is made of a high reflectivity material such as Ag. Rather, the light rays are scattered from the irregular surface to disappear.
Accordingly, there have been required in the art nitride semiconductor LEDs and a fabrication method thereof which can minimize light loss as well as maximize luminous efficiency by using a suitable reflector structure.